In gas turbines combustion air is usually compressed in a multistage compressor and then guided to a number of gas-turbine burners which are arranged on a combustion tube typically guided in an annular shape around the turbine axis. In the effort to carry out combustion in a gas turbine while generating as little NOx as possible, so-called DLN (dry low NOR) systems have been proven. In such systems there are a number of main swirl generators, also referred to as the main swirl generator arranged around a pilot plug in each gas-turbine burner, in which fuel—usually natural gas—is swirled strongly with air to create a stable pilot flame. The compressed air flows through the main swirl generators and is mixed with the fuel in the main swirl generators, in order to burn downstream outside the main swirl generators in a combustion tube. The gas heated up by the combustion is subsequently directed into a working turbine to do work by expansion.
To keep a burner section of a gas turbine compact, the combustion air compressed in the compressor is usually guided to the gas-turbine burners located radially further outwards so that the compressed air is guided outwards against a direction of flow in the main swirl generators along the gas-turbine burner or their burner casings. To enable it to flow into the inlet flow openings of the main swirl generators, the flow of the compressed combustion air must undergo a reversal in its direction and in doing so flow around a deflection edge of the burner casing and/or of the main swirl generator facing away from the combustion tube.
The reversal of direction and the flow around a deflection edge can lead to a flowback occurring between the main swirl generators and the burner casing which may possibly even continue into small areas within the main swirl generators. A detaching of the flow at or from the deflection edge can lead to the same effect. This results in an uneven distribution of the flow through the main swirl generators, with the most problematic area—in relation to a radial inner pilot plug—being the radial outer zones of the main swirl generators. The uneven air mass flow and the lower flow speeds resulting therefrom in these problematic zones results during the injection of fuel into these zones in very rich mixtures, for which a high risk of flame flash back exists. The flowback zones, which are also always associated with a transient behavior, increase the tendency to thermo acoustic combustion chamber vibrations.
U.S. Pat. No. 4,689,961 describes combustion chamber equipment mt with swirl generators and also a cup-shaped bulge with a passage in which the injector and the swirl generator and also an inflow means are accommodated.
US 2003/0110774 A1 discloses a gas turbine with main flow generators having an inflow opening.
To solve this problem an attempt has been made to introduce increased combustion air within the main swirl generators in order to make the rich areas leaner. In a similar way only a small proportion of fuel was entered into the problem zones, which leads to a worse mixture and thereby to a higher NOx emission.